The present invention relates to a seal between rotor blade platforms and stator vane platforms, and in particular to a seal between turbine rotor blade platforms and turbine stator vane platforms of a turbomachine, for example a gas turbine engine.
A turbine of a gas turbine engine comprises one or more stages of turbine rotor blades arranged alternately with one or more stages of turbine stator vanes. Each of the turbine rotor blades comprises a root, a shank, a platform and an aerofoil. The turbine rotor blades are arranged circumferentially around a turbine rotor and the turbine rotor blades extend generally radially from the turbine rotor. The roots of the turbine rotor blades are located in axially, or circumferentially, extending slots in the periphery of a turbine rotor. The platforms of the turbine rotor blades together define the inner boundary of a portion of the flow path through the turbine. In some instances the turbine rotor blades may have shrouds at their radially outer ends to define a portion of the outer boundary of the flow path through the turbine. The turbine stator vanes also have platforms at their radially inner ends and shrouds at their radially outer ends.
Generally, the platforms of the turbine rotor blades and the platforms of the turbine stator vanes have upstream and downstream portions, which extend axially towards each other. Thus the turbine rotor blades in a stage of turbine rotor blades have upstream portions of the platforms, which extend in an upstream direction towards a downstream portion of the platform of the stage of turbine stator vanes immediately upstream of the stage of turbine rotor blades. The stage of turbine stator vanes immediately upstream of the stage of turbine rotor blades has a downstream portion of the platform, which extends in a downstream direction towards the upstream portion of the platforms of the turbine rotor blades and the downstream portion of the platform of the turbine stator vanes is arranged radially around the upstream portions of the platforms of the turbine rotor blades.
Similarly the turbine rotor blades in the stage of turbine rotor blades have downstream portions of the platforms, which extend in a downstream direction towards an upstream portion of the platform of the stage of turbine stator vanes immediately downstream of a stage of turbine rotor blades. The stage of turbine stator vanes immediately downstream of the stage of turbine rotor blades has an upstream portion of the platform, which extends in an upstream direction towards the downstream portions of the platforms of the turbine rotor blades and the downstream portions of the platforms of the turbine rotor blades are arranged radially around the upstream portion of the platform of the turbine stator vanes.
A clearance is formed between the upstream portions of the platforms of the stage of turbine rotor blades and the downstream portion of the platform of the upstream stage of turbine stator vanes and a clearance is formed between the downstream portions of the platforms of the stage of turbine rotor blades and the upstream portion of the platform of the downstream stage of turbine stator vanes.
These clearances control the amount of cooling air flowing from within the interior of the turbine into the flow path through the turbine and control the flow of hot gases from the turbine flow path into the interior of the turbine. The platforms of the turbine rotor blades and turbine stator vanes overlap to provide a smooth flow line for the inner boundary of the flow path through the turbine.
A problem with this arrangement is that these clearances change with temperature, speed of rotation of the turbine rotor etc. The clearances increase in dimension at some operating conditions. This increase in clearances leads to excessive cooling flow through the clearances and hence a loss of efficiency of the turbine and the gas turbine engine. Additionally there is a change in the clearances, and their effectiveness, due to wear of the platforms and/or relative movement between the turbine rotor and turbine stator.